Driving me mad

["Pete Shew" <ukha_d@xxxxxxxxxxxxxxxxxx>]

I have a sound that I cant locate. It is a "meem" rather than a
"peep" and seems to be around 440Hz (A above middle C, if my
musical memory serves.)

It occurs every 173.5 seconds!

It appears to be above the kitchen, but can't be localised. In the room
above it can be heard more faintly.

It's fairly quiet, so can't be heard if there is TV, radio, washing up etc.

It continues even with the power turned off at the main breaker !!!

The only other power is the battery to the alarm system. The control box
and sounder are some distance away and the sound cannot be heard there, but
there is a IR detector near the sound.

Any suggestions at to what it might be or a method of finding it gratefully
received.

Pete